I describe an experimental apparatus used to perform deformation experiments
relevant to volcanology. The apparatus supports low-load, high-temperature deformation
experiments under dry and wet conditions on natural and synthetic samples. The
experiments recover the transient rheology of complex (melt ± porosity ± solids) volcanic
materials during uniaxial deformation. The key component to this apparatus is a steel
cell designed for high-temperature deformation experiments under controlled water
pressure. Experiments are run under constant displacement rates or constant loads; the
range of accessible experimental conditions include: 25 - 1100 °C, load stresses 0 to 150
MPa, strain rates 10⁻⁶ to 10⁻² s⁻¹, and fluid pressures 0-150 MPa.
I present a suite of high-temperature, uniaxial deformation experiments performed
on 25 by 50 mm unjacketed cores of porous Φ∼0.8) sintered rhyolitic ash. The
experiments were performed at, both, atmospheric (dry) and elevated water pressure
conditions (wet). Dry experiments were conducted mainly at 900 °C, but also included a
suite of lower temperature experiments at 850, 800 and 750 °C. Wet experiments were
performed at ∼650 °C under water pressures of 1, 2.5, 3, and 5 MPa, and at a fixed PH2O
of ∼2.5 MPa for temperatures of ∼385, 450, and 550 °C. During deformation, strain is
manifest by shortening of the cores, reduction of porosity, flattening of ash particles, and
radial bulging of the cores. The continuous reduction of porosity leads to a dynamic
transient strain-dependent rheology and requires strain to be partitioned between a
volume (porosity loss) and a shear (radial bulging) component. The effect of increasing
porosity is to expand the window for viscous deformation for dry melts by delaying the
onset of brittle deformation by ∼50 °C (875 °C to 825 °C). The effect is more
pronounced in hydrous melts (∼0.67 — 0.78 wt. % H₂0) where the viscous to brittle
transition is depressed by ∼140 to 150 °C. Increasing water pressure also delays the onset
of strain hardening due to compaction-driven porosity reduction. These rheological data
are pertinent to volcanic processes where high-temperature porous magmas I liquids are
encountered (e.g., magma flow in conduits, welding of pyroclastic materials).
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU./2738 |
| Date | 05 1900 |
| Creators | Robert, Geneviève |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | 2593601 bytes, application/pdf |
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